Braze bonding is widely used for bonding of copper parts. There is a case in which many parts are braze-bonded in a batchwise manner. In addition, when water or the like is let to flow in a part, a bonded part will have a seal function. When many parts are bonded in a batchwise manner with sealing properties, it is important to confirm the state of braze bonding, and it is necessary to recognize a braze bonding length (so-called seal length).
Conventionally, in an inspection of a braze-bonded part, the braze-bonded part is cut, and the presence/absence determination of a defect by visual observation (cross-sectional observation) with use of a microscope or the like, the defect detection by an ultrasonic flaw detection method, or the presence/absence determination of a defect by visual determination of a radiography image, is performed.
However, when only such conventional defect presence/absence determination is performed, the following problems will arise.
Here, a water-cooling coil of an electrical rotating machine is taken as an example, wherein many hollow copper wires and solid wires are braze-bonded together to a copper-made water chamber part. In the braze bonding, in order to infiltrate molten solder by utilizing a capillary phenomenon of the molten solder, a narrow gap of 0.05 mm to 0.25 mm is usually adopted as the gap between copper wires. A defect of braze bonding (for instance, a part where solder failed to infiltrate, a bubble occurring in solder, a shrinkage cavity, or a crack of solder), which occurs in such a narrow gap, will necessarily become smaller than the narrow gap, and it is not possible to quantitatively evaluate the braze bonding length by visual observation or the like.
There are various modes in shape of defects occurring due to braze bonding. In order to secure a seal length, it is necessary to quantitatively evaluate, regardless of the shape of a defect, the bonding length of solder which fills the narrow gap at the braze-bonded part.
However, in the conventional defect presence/absence determination, although qualitative determination, such as determination as to whether there is a defect in a braze-bonded part, can be performed, quantitative determination as to how long braze bonding is made is not performed.
This being the case, in order to evaluate a seal function by braze bonding, there is a demand for an apparatus and method for performing not only qualitative evaluation, such as simply confirming a braze bonding state, but also quantitative determination of a braze bonding length (so-called seal length).